The optical force is one of the most fundamental properties carried by light. This force is generally considered too small for macroscopic practical use. Yet in the microscopic world, optical tweezers have been widely used to manipulate atoms and micron-sized dielectric particles in free space.
One natural step forward would be exploiting this principle as a driving force in solid state devices such as electromechanical systems. Indeed, recent experiments have elucidated the radiation force of light in high finesse optical microcavities (see references 1 to 3). However, the large footprints involved in these optical microcavities fundamentally limit the scaling of devices down to nanoscale dimensions where exciting quantum phenomena such as macroscopic quantum coherence, generation of squeezed states and optical entanglement start to manifest.
Harnessing optical forces on chip would bring transformational advances in electromechanical systems by offering efficient and ultrahigh bandwidth optical coupling to the sub-micron scale devices. This new transduction is fundamentally distinctive from conventional charge based schemes predominately employed in today's solid state devices. The forces of light stem from two major mechanisms, namely radiation pressure and transverse gradient force.
Radiation pressure induced forces have been extensively studied in the high finesse optical cavities, where light field is confined inside the cavity and the moment of light is transferred to the mirror forming the cavity and applies a perpendicular force to the mirror. Analogously, radiation pressure is also detected in the high finesse microspheres or disk resonators6. The transverse gradient force, on the other hand, results from the lateral gradient of propagating light field and therefore applies a transverse force to a dielectric body. Recently it was theoretically predicted that this seemingly small force could be significant in photonic structures due to enhanced light density in submicron scale photonic waveguides (see reference 4).
Recent theories predicted that the optical force can be enhanced in a photonic waveguide without the aid of a cavity and can be directly used for electromechanical actuation; however, on-chip detection of the force has been a significant challenge, primarily owing to the lack of efficient nanoscale mechanical transducers in the photonics domain.